There are certain parameters on which you can judge the college. The most important are it's fee, the syllabus and whether campus recruitment program is there or not.
Anyway these details will only be available when you request brochures from them which can be done online.
In Bangalore other than Gems B School there are some equally good institutions for BHM. They are - Garden City University, SJES College of Management studies and AIMS institute.
You can get detailed information about them at -
You can request for information brochures also at above site.
Similarly in Chennai also other than Amrita College there are some top ranked institution like AIMS, MIHMCT, IIB, AMIHMCT etc. If you want the list of these top schools for BHM in Chennai then you can get their addresses and email at -
You can yourself see the details of these colleges as well as their rank based on comments by people or other parameters.
Please remember that among the few top schools it becomes difficult to tell number one but you have to see from your point of view which one suits you best in terms of fee, syllabus and future job prospect.
Knowledge is power.